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Industrial mining and processing of zinc and copper ore in Flin, Flon MB/ Creighton, SK by the Hudson Bay Mining and Smelting Co. Limited (HBMS; a division of Hudbay Minerals Inc.) has led to the enrichment of the surface soils with heavy metals such as copper (Cu), zinc (Zn), and cadmium (Cd) and soil acidification from sulfur dioxide. In addition to forest dieback resulting from heavy metal contamination and soil acidification, forest fires and timber harvests have resulted in considerable loss of native forest. As a soil amendment for revegetation, the community-lead Flin Flon/ Creighton Green Project has been adding dolostone to the surface of the soil. This project has resulted in varying and unexplained levels of success with significant re-growth of trembling aspen (Populus tremuloides) and white birch (Betula papyifera) at some sites, with a lack of response at others.
This study was conducted to examine the effects of the dolostone used in Flin Flon, MB/ Creighton, SK on the soil properties, metal availability, and plant growth to understand the variable response of liming at the site. In addition, metal uptake, low molecular weight organic acids in the soil, changes in pH, and changes in available metals were analyzed after the growth of a metal hyperaccumulating plant Pelargonium sp. ‘Frensham’ and two metal excluding plants Silene vulgaris and Agrostis capillaris to determine the interactions of metal-tolerant plants with the soils after liming. These plants were chosen to examine the effects of the different mechanisms of metal tolerance on metal uptake, mobility, and bioavailability in contaminated soils after liming. Limed and non-limed soils from a responsive site at Knight North (KN) and an non-responsive site at Second Valley North (SVN) were collected from Flin Flon, MB/ Creighton, SK, along with a reference soil from an undisturbed boreal forest east of the smelter, for a growth trial.
Liming had a positive effect on the soil, increasing the pH, decreasing the available fraction of metals, and increasing plant growth. On the SVN site, the pH only increased from 4.01 to 4.25, while the available NO3- and exchangeable calcium (Ca2+) and (Mg2+) remained low, indicating the dolostone had not dissolved or had leached out. Subsequently, the available metal fraction decreased, however Zn2+ remained at 296.3 mg kg-1 contributing to the toxicity of the soil. On the KN site, the initial NO3- was the highest for all the soils, and the dolostone increased the pH from 3.36 to 5.10 while increasing the exchangeable Ca2+ and Mg2+ above the reference soil. The increase in pH caused by the dolostone lead to a substantial decrease in the available metal fraction on this soil and increase in plant biomass. Plant growth increased from the KN non-limed < SVN non-limed < SVN limed < KN non-limed < reference soil. The lower response to the lime at the SVN site was attributed to the lack of dolostone dissolution on site and/or leaching of Ca and Mg, the dense sod matt of A. capillaris inhibiting germination of other plant species, as well as the low nutrient status of the soil.
Overall plant growth had a positive effect on the soils, especially the metal-excluders S. vulgaris and A. capillaris in the SVN soil. Both plants significantly increased the pH of the soil and decreased the available fraction of Al3+ in the non-limed soil, and Cu2+ and Al3+ in the limed soil. Pelargonium sp. ‘Frensham’ did not significantly change the pH of the soil, however the plants accumulated high concentrations of Cu, Zn, Cd and Al in the plant tissues; and P. sp. ‘Frensham’ decreased the available fractions of Cu, Zn, and Al in the SVN limed soil, and Zn in the KN non-limed soil. For the three plant species used, liming decreased the concentration of heavy metals in the shoots. Where plants established in the non-limed soils, the concentration of heavy metals in the shoots was larger than in the reference soil and limed soils, except for P. sp. ‘Frensham’ with Al. On the SVN soils, liming increased the concentration of Al in the shoots near the threshold of hyperaccumulation at 1000 mg kg-1 dry weight. For the most part, higher shoot concentrations of heavy metals in the non-limed soils indicate that lime should be used to decrease the uptake of heavy metals into the aboveground biomass, even if vegetation is present in the soil without lime, to control the transfer of metals to other components of the ecosystem.

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